The present invention relates to an electro-luminescent display, and more particularly to a method for manufacturing a pixel area of the same.
Flat display technology has been significantly advanced recently, in part because manufacturing thin film transistors on a substrate, such as glass, has become a mature skill. This facilitates the development of active matrix type display devices. In addition to liquid crystal materials, which need a backlight source, an electro-luminescent device, such as an organic light emitting diode (OLED) that can emit light itself, is intensively researched. Because of the self light emission, a display equipped with electro-luminescent devices is brighter than a backlit liquid crystal display.
FIG. 1 is a cross-sectional view of a conventional electro-luminescent display device 10 with a thin film transistor (TFT) area 110 and a pixel area 120. The electro-luminescent display device 10 includes a substrate 130, a silicon nitride buffer layer 132, a silicon oxide buffer layer 134, gate oxide layer 136, inter-layer dielectric (ILD) layer 138, indium-tin-oxide (ITO) layer 140, organic light-emitting layer 142, and cathode layer 144.
In the process of forming the electro-luminescent display 10, the gate oxide layer 136 and the ILD layer 138 originally deposited in the pixel area 120 need to be removed for they may reduce light-emission intensity. A photolithography step is performed to define a window exposing a part of the oxide layer 136 and the ILD layer in the pixel area 120. The exposed part is then etched away to expose the underlying silicon oxide buffer layer 134 in the pixel area 120. The ITO layer 140 and the organic light-emitting layer 142 are subsequently deposited thereon to from a structure as shown in this figure.
This conventional fabrication process has a drawback of poor level uniformity. Because the etch selectivity of the gate oxide layer 136 and its underlying silicon oxide buffer layer 134 is very low, it is difficult to properly control the end point of the etching process. This would cause an uneven surface 160 of the silicon oxide buffer layer 134 in the pixel area 120. As a result, the subsequently formed ITO layer 140 and organic light-emitting layer 142 would also have uneven surfaces. This greatly degrades the performance of the electro-luminescent display device 10.
What is needed is an electro-luminescent display fabrication process with an improved level uniformity of the layers formed in a pixel area.